Electrophonic sound reproduction



July 5, 1932, R. M. HILL ELECTROPHONIC SOUND REPRODUCTION Filed Aug. 2l, 1926 Patented July 5, 1932 PATENT OFFICE ROGER -H'ILL OF WASHINGTON, DISTRICT 0F COLUMBIA iinnc'rnorrromrc SOUND azzxriaonncfrroisrV Application mea August a1, 1926. serials. 130,542.

This invention relates to the reproduction of sound and particularly to the reproduction of sound .by electrical means.

It is the principal objectV of this invention i to provide a method of and apparatus for reproducing sound by electrical means whereby an operator may vary the characteristics of transmitted sounds in certain ways as they are being reproduced to produce variouseffects or to correct for known defects in the transmitted sounds.

Other objects Voi? this invention and certain features of novelty will be apparentrom the following description taken in connection with the drawing, in which: i i

Figure 1 shows one orm ofV apparatus in which this invention is embodied; 4

Figure 2 is a diagram showing graphical- 1y what may be. accomplished by this invention in connection with one form of sound transmitting medium, namely, a phonograph record; and f v Figure 3 is a diagram showing how anincrease in volume may be achieved without a corresponding increase in power. Y

In order that a clearer understanding of the scope and purposes of this invention may be had, it is deemed advisable here to give a brief discussion of existing conditions and difficulties which it isintended to improve or remedy. j y

Primarily this invention has to do with public exhibitions and at the present time is thought to be particularly adapted to be used in connection with the projection of motion pictures, though it is in no .wise limited to such employment, being suitable for vaudeville shows, concerts and various other formsof public entertainmentV as well as for private amusement.

The invention also is illustrated and described principally in connection with thereproduction of sound from a phonograph record as a sound transmitting medium, but willV be understood to be equally applicable to use with reproduction from a. radio receiving set, a piano, violin,,guitar, flute, saxophone or'practically any sound producing medium. t

The invention will rst be discussed in connection with a phonograph` record, as, according to the present principal purposes of this invention such a medium is particularly adapted to be used ,with the projection of motion pictures. Records maybe madeup for Vand shipped with a given set ofilms comprising a p1cture. These 1 records with proper control, as by use of this invention, may be used to give similar ei'ects and to replace the large and expensive orchestras which are now employed to accompany these pictures. I

The usual phonograph record, as made, does not-give a true reproduction of sounds as theywere originally played'ior making the record. This is due to the fact that the sounds are not recorded on the record eXactly as they are played. For instance, the bass parts are damped in relation to the altoand treble parts. To record bass orlow frequency T' vibrations in their proper ratio would produce such wide swings of the recording needle due to the relatively greater amplitude of vibration of the bass notes, that the needle would cut into an adjoining groove. A remedy for this would be to space the adj acent grooves further apart and allow the needle to make a full swing, but this would produce a groove with sharp bends. The reproducing'needle wouldA not readily follow the v groove past the bends and hence would cause the record to be slowed ydown if not altogether stopped. The ordinary record, therefore, as is well-known, is a compromise. The various. parts betwen 200 and 5000 vibrations per second are all'present on the record, but

not in their true volume ratios as played. The curve R of Fig. 2 representsA the compromise recording scheme adopted by practically all the recording companies at the present time. Various attempts have been made to rectify these ydefects of recording in the reproducer and have met withmore or less success through changes made in the reproducing diaphragms, hornsV and other mechanical parts. lt is the purpose of this invention to remedy these defects by electrical means.

The scheme of recording also often fails to bring out the proper contrast between successive loud and' soft passages. VIt is, therefore, a further purpose of this invention to remedy this defect.

The apparatus which applicant has designed to correct the above enumerated defects, provides in addition a playability in reproducing, thus enabling the operator to reproduce various parts in a greater ratio to other parts than that in which they were originally played, to accentuate all parts either by damping-or increasing,V or to bring out one voice or instrument from a number of others present on the record. .ByV the employment of this invention alsothe parts of a duet, tercet, quartet, etc.` may be separated and localized whereby the effect of one voice heard in one location and another voice'heard in another location at Ythe same time, may be obtained from a single record in which the voices were recorded simultaneously.

Referring more .particularly to the drawing which illustrates one of any number of forms of apparatus known to applicant for carrying out this invention, V10 denotes a phonograph or other device for rotating a record. A microphone 11 carrying a needle is held in operative relation to the record as the same is turned. Themicrophone is in a circuit 12 having a source of electrical energy 13 and a primary coiljla of a transformer T. It is evident that other instruments might be used with the microphone or that the circuit 12 might be the outputv circuit of a radio receiving set.

The secondary'circuit 17 contains a transformer coil 15 and one or more sound receivers or loud speakers 16, 18. These receivers may be'dissimilar or may be similar if means is provided to change their characteristics. F or this purpose, tone filters 19, 20 may be employed with one or more of the receivers and have control switches 21, 22 for inserting or removing the tone filters from the speaker or receiver circuit. Thespeakers may be located at any desired points while the control switches may conveniently be mounted on a panel P which also serves to assemble various other controls to vbe described below. Il`his compact assembly of controls makes the apparatus easily playable like a pipe organ for instance and enables one operator to producev the various eects at will. i

Referring again to the speakers, it is to be noted that by proper selection of the same or by the insertion of appropriate tone filters an almost complete correction of the errors of. recordingmay be obtained. The curve R of yFigure 2 as stated represents the characteristics of the recording apparatus. The other speaker or combined speakers may be selected to have characteristics such as are shown by curve WP. To explain this more fully, it has been found that the treble parts are recorded in substantiallyr their.' correct ratios while theV bass up' to about 500 vibrations per second is recorded in an incorrect ratio. With a speaker which responds only to vibrations up to 500 per second and having the characteristic curve T, the errors of recording may be largely rectified as shown by the curve N. 1t has even been found that a single speaker may be made which will rectify the bass and faithfully reproduce the treble, but two speakers are preferable as they lend playability to the instrument represented by the entire apparatus employed.

. Either one or both speakers (in case only two speakers are employed) may be cut into the secondary or receiver circuit 17 by means of switches 25 or 26 or make push buttons 27 or 28. The switch and push button are mounted on the panel P and are arranged in parallel sothat by use of the push button the circuit may be closed for short intervals and by use of the switch the circuit may be closed for longer intervals when the operator wishes to devote his hands to other keys. When the speakers have dierent characteristics the total volume of sound produced by them is greatly increased by cutting in a second one of them without any increase in the power used to operate them. This is due to the fact that the second speaker responds to low frequency vibrations (in case the bass speaker is cut'in) which are being transmitted through the receiver circuit, but to which the speaker first used is only slightly responsive.4 This is shown graphically in Fig. 3. However, if desired, the power may be increased when a speaker is added. This may be done by increasing the current in the primary circuit. For this purpose lswitches 30, 31, .one foreach speaker, located where they can be operated with one or the other of the switches 25, 26 will serve the purpose. The related switches 25, 30 and 26, 3l may be'constituted as double pole switches as illustrated so they may be readily operated together. It will be obviousthat when either one of the double pole switches is thrown in,

. the primary circuit will be, completed and one speaker set `into voperation and when the other double pole switch'is thrown in the total resistance of the primary circuit will belessened and the secondspeaker set into operation. Variable resistances 32, 33 may also be inserted near the switches to regulate the yamount of increase of the current.

F or damping, increasing, or otherwise varying the total volume of sound from one or several of the speakers, other control may Vbe employedV and such Controls are also mounted on the panel P. The controls are shown in the main receiver circuit but could as well be placed where they would control each speaker separately instead 'of collectively as shown in F ig. l. For damping a soft'pedal circuit S is used.L It consists of a variable resistance 35and a break push button 86.- By pressingV the button, the resistance is cut in to the circuit. For increasing the volume a loud pedal circuit W is used. It consists of a variable resistance 37 and a make push button 38.

A tremolo veffect may be obtained by rapidly cutting in and cutting out resistance.V This may be provided by a tremolo circuit V. It consists of a variable resistance 39, a make push button 40 and a vibrator 41. The vibratorl comprises a magnet 41a, a battery 41?), a make push button 410 and a spring supported blade 41d. The vibrator is set inv operation by pressing button 410. @bviously a switch might be used if it is desiredto keep the vibrator operating continuously. rThe blade lla? of the vibrator alternately shorts out and reinserts resistance 39 beyond push button 4:0. By completing the circuit through the push button alternate short circuits across the resistance 39 are produced and due to the rapidity with which the vibrator causes the shorts a tremolo eect is produced through the speakers.

The microphone of the primary circuit may obviously be used on other sound producing media than a phonograph record. It may, in fact, be employed with any source of sound producing vibrations or impulses.

It is not desired that this invention be limited to the exact embodiment describechfor applicant is well ,awareV that the invention may be carried out in many other embodiments Within the scope of the appended claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

l. The combination with a means for producing electrical sound impulses, of a pluj rality of receivers for transforming the impulsesinto sound, means under the instant control of an operator for causing the impulses to be transmitted to a given one or any number of the receivers simultaneously during the continued reception of impulses by the receivers and mechanical means for producing a tremolo e'ect during the operation of any one or all of said receivers.

2. The combination with a source of electrical sound producing impulses, of a plurality of receivers each of which is responsive to a given range of impulse frequencies, means Within the instant control of an operator for putting a given one or all of said receivers in communication with the impulses during the continued emanation of impulses from said source and a plurality of resistances arranged in parallel, one of which is inserted simultaneously with a corresponding receiver to cause an increase in current needed for the additional receiver.

3. In a system for reproducing sound from' engraved records having known deciencies, in combination, a primary circuit embracing a source of power and a transmitter operating upon said record, a secondary circuit embracing a plurality of loud speakers or receivers of dierent characteristics so selected as to effectively compensate for the known deficiencies in recording, and double pole switches one for each speaker for inserting the speaker in the secondary circuit and si-v multaneously increasing the current in the primary circuit to accommodate the added speaker.

4. A system asset forth in claim 3 which further includes in combination a variable resistance and a push button in parallel therewith in the secondary circuit for each speaker for changing the volume of sound emanating therefrom.

5. The system as set forth in claim 3 which further includes in combination a tone filter in Vthe secondary for each speaker and means to eliminate the effect of the tone filters.

6. The system as set forth in claim 3 which further includes in combination an interrupter or vibrator in the secondary circuit serving allv such speakers as may be in operation and a terciary circuit for supplying power to operate said interrupten In testimony whereof I hereunto aiX my signature.

vROGER M. HILL. 

